This invention relates to a simple printing device capable of presenting clear print-out of informations on recording mediums.
Heretofore, a printing device which prints out operational results of electronic computers, and so on has been so constructed to make a clear distinction, for example, between positive (+) numerical data and negative (-) numerical data by printing the positive numerical data with black ink and the negative data with red ink so as to enable anyone to clearly recognize informations printed on the recording medium.
In order to carry out such segregated printing as mentioned above, the conventional printing device has been provided with a simple printing ink tape or ribbon which impregnates therein both red and black inks in a discrete section for each, and the printing operation is carried out by selecting either a red ink ribbon or a black ink ribbon through an electrically or mechanically controlled device. In this ink ribbon, frequency of printing informations with the red ink ribbon is far less than that of printing with the black ink ribbon with the consequence that, on many occasions, even when the black ink ribbon becomes exhausted, the red ink ribbon is still usable. Accordingly, when the black ink ribbon is to be replaced, the still usable red ink ribbon is discarded, which is a considerable waste against saving of resources.
Moreover, the minus (-) symbol has heretofore been printed either in red on the symbol place (as shown by m in FIG. 1A in the accompanying drawing to be referred to later), or by causing the symbol to float in front of the numerical data (as shown by m in FIG. 1B). In any of the above-mentioned cases, however, the ink ribbon is required to be changed over, which slows down the printing speed, requires a separate mechanism for changing-over of the ink ribbon, and so is liable to complicate the printing mechanism as a whole.